Heat sink



FIG. 1 is a perspective view of a heat sink of my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken line showing of the heat sink is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a heat sink, as shown and described. 